cardiac muscles; the heart as a pump and function of valve

Question 1

cardia rhythmicity

Answer 1

trasmiting action potentais through the cardiac muscles to cause the hearts rhythmical beat

Question 2

three types of cardiac muscles

Answer 2

1. atrial muscles
2. ventricle muscles
3. excitatory and conductive muscle fiber

Question 3

how excitatory and conductive fibers contract?

Answer 3

the contract by automatic rhythmical electrical discharge in the form of action potential or conduction of action potential by the heart that creates an excitatory system that controls the systematic beating of the heart

Question 4

Explain left ventricle rotation

Answer 4

the left ventricle twists during a systole . It has muscle fiber layers. The subepicardial (outer) layer spirals towards right and the subendocardial (inner) spirals towards the left which causes the apex of the heart to move clockwise and the base to move anticlockwise
During systole the ventricle moves downwards the apex and after systole it recoils untwist during relaxation diastole

Question 5

Cardiac muscle is a syncytium

Answer 5

the cells if cardiac muscles are joined together by intercalated disks. These intercalated disk join the cardiomyocytes by making a permeable connection between the cells (gap junction). The ions move across this junction to neighbouring cells which also allows action potential to move across each cell. Cardiac muscle is a syncytium of many heart cells that are so interconnected that when one cell gets excited all the cells receives the action potential

Question 6

two syncytia

Answer 6

atrial syncytia and ventricle syncytia

Question 7

What separatees atrium and ventricle

Answer 7

fibrous tissue that surround the atrioventricular valve.

Question 8

how action potential spreads from atria to ventrucle

Answer 8

by AV bundle

Question 9

Action potential recorded in ventricle

Answer 9

stays about average of 105 millivolts. Intracellular potential goes from a negative between beats of -85 millivolt to positive of +20 millivolt. After spike the membrane remains depolarized for 0.2 secs, and repolarizes again.

Question 10

Causes of long action potential in cardia muscles

Answer 10

1. Contains slow calcium channels, which open late and then remain open for a tenth of a second intitiates the contraction.
2. Immediately after the onset of a action potential the permeability of positive K ions decrease by five fold, which stops the efflux of +vely charged K ions during action potential and prevents early return of action potential to its normal level

Question 11

Phase 0

Answer 11

Cardiac cell stimulated and depolarizes, making the action potential positive to 20millivolts. Voltage gated fast sodium channels open and Na efflux increases

Question 12

Phase 1

Answer 12

initial repolarization- Na channels close and potassium leaves the cell

Question 13

phase 2

Answer 13

initial repolarization occurs and then action potential plateaus causes of increase calcium permeability and decrease K permeability. The Ca channels open at phase 0 &1 and potassium channels close, which stops the efflux of K ions to the outside

Question 14

Phase 3

Answer 14

opening of K channels causes efflux of K ions and closing of Ca channels and cello membrane return to normal action potential

Question 15

Phase 4

Answer 15

resting membrane potential averages about -80to -90

Question 16

Velocity if signal conduction in heqrt

Answer 16

0.3 to 0.5 m/sec which is 1/250 the velocity of a large nerve fiber and 1/10 of a skeletal muscle. 4m/sec in purkinjee fiber

Question 17

refractory period ?

Answer 17

it is the interval of time in which the cardiac impulse cannot re excite an already excited cardiac muscle

Question 18

Values of refractory period

Answer 18

0. 25-0.30 second for ventricles

0. 15 for atrial

Question 19

Relative refractory period

Answer 19

Addition 0.05 second during which an excited muscle is more Hard to re-excite but it can still be re excited with a very strong excitation signal

Question 20

Explain the process of excitation that happens in same way in skeletal ma

Answer 20

he action potential reaches the the interior of cardiac muscles, from there jt travels to the membranes of longitudinal T tubules then it acts on the membrane of sarcoplasmic tubules which causes the release of calcium ions into the muscle sarcoplasm and in few thousandth of seconds actin and myosin filaments slide over each other to cause muscle contraction

Question 21

What differently happens in cardiac muscle than in skeletal muscle during muscle contraction

Answer 21

Calcium ions from T tubule also diffuse into the sarcoplasm, which opens the voltage dependant calcium channels in the membrane of T tubule, calcium entering the cell then activates calcium release channels or ryanodine receptors in the sarcoplasmic reticulum triggering the calcium ions to be released in the sarcoplasm

Question 22

Cardiac cycle

Answer 22

the events from the begging of one heartbeat to the begging of the other is called as cardiac cycle

Question 23

Explain where cardiac cycle in events

Answer 23

starts from sinus node which is present on the superior lateral wall of right atrium from where the superiors vena cave enters then passes to both atria then to Av bundle and then to ventricles.

Question 24

Why atria are prime pumpers

Answer 24

there is a delay of more than 0.1 second during the passage of each cardiac impulse from atria to ventricle . So the atria contracts ahead of ventricle

Question 25

Period of rapid filling of ventricle

Answer 25

During a ventricular systole, large amount of blood accumulate in right and left atrial due to closed AV valve. During ventricle diastole, the pressure inside the ventricles decreases and the already made pressure in the atria during ventricle systole causes the opening of AV Valve and rapidly fills the ventricle with blood

Question 26

The three thirds of diastole in which the blood fills the ventricle

Answer 26

in healthy humans the period of rapid filling of ventricle lasts for the first third of the diastole. The mid third is when a very small amount of blood passes to ventricles which the the blood coming from veins into the atria and it passes directly into the ventricle. The last third is when the atria contracts and give additional thurst and fills the heart with the 20% of blood to the heart

Question 27

What happens to people heart disease

Answer 27

In cardiac fibrosis or diabetes mellitus the ventricles stiffen up this causes less blood to fill the ventricles during the early diastoles and require more volume or more filling from later atrial contraction

Question 28

Period of isovolumic contraction

Answer 28

when the ventricle contracts, it takes 0.2 to 0.3 second to to build up sufficient pressure to push the semilunar valves. In this time contraction is occurring but no emptying is done that is the muscle tension is increasing but no muscle shortening is happening

Question 29

period of ejection

Answer 29

when the pressure of left ventricle increases more than 80 mm Hg the pressure opens the semilunar valves and the blood goes into the aorta and pulmonary artery. 60% of the blood is ejected at the end of the diastole, 70% is ejected in First third Called period of rapid ejection and the 30% is ejected in the rest of the two thirds called the period of slow ejection

Question 30

Period of isovolumic relaxation

Answer 30

at the end of systole, ventricle relaxation behinds and the pressure decreases in the ventricles. The aorta and pulmonary artery valves to be closed when the hood in send back because of pressure created in the distended arteries. 0.03 to 0.06 second is taken More by ventricle to relax, even though the volume isn't changing

Question 31

End diastolic volume

Answer 31

When the blood enters the ventricle the increase In volume of each of the ventricle is 110 to 120 ml called as end diastolic volume

Question 32

Stroke volume output

Answer 32

when the ventricles get empty the volume decreases by about 70ml stroke volume output

Question 33

End systolic volume

Answer 33

remaining volume in each ventricles is 40 to 50ml called end systolic volume

Question 34

Ejection fraction

Answer 34

the fraction of end diastolic volume that is ejected is 60%. It is clinically used to asses cardiac systolic pumping

Question 35

where are papillary muscles in the heart are founds

Answer 35

they are attached to the vane of av valves by the chordae tendineae.

Question 36

Functions of papillary muscles in heart

Answer 36

They papillary muscles contract when the ventricle walls contract, they pull on vanes of the valve pulling them inwards into the ventricle preventing them from bulging too much into the atria

Question 37

preload

Answer 37

the degree of tension in the muscle when it becomes contracted is pre load

Question 38

after load

Answer 38

the load against which the muscles exerts the contractile force

Question 39

basic mechanisms of regulation of heart pumping

Answer 39

1. intrinsic cardiac pumping regulation in response to the change in the volume of blood flow 2. regulation of heart beat through the autonomic nervous system

Question 40

Frank sterling mechanism of the heart

Answer 40

the intrinsic ability of heart to manage blood flow is called Frank steeling mechanism of heart. It means the greater the heart muscle is stretched during blood filling, the greater the force of contraction, the greater the quantity of blood flown into aorta

Question 41

Effect of K ions on hear function

Answer 41

increased level of K ions in extracellular fluid makes the heart dilated and flaccid, also decreases the cardiac impulses travelling from atrial to ventricle through Av node. Only 2-3 times more value than normal of K ions can cause abnormal rhythm and death

Question 42

Why k ions have that affect

Answer 42

it lowers the membrane potential by causing depolarization, low membrane potential means Low action potential intensity and intensity muscle contraction weakens

Question 43

Effect of Ca ions

Answer 43

opposite effect to K ions, it causes spastic contractions